The present invention relates to a clearance adjuster, and more particularly relates to a clearance adjuster for adjusting the clearance in a clutch actuation system for a vehicle in which a clutch pedal drives a clutch by a cable assembly. In its widest concept, however, the clearance adjuster of the present invention can be used for a wide range of devices.
The background of the present invention will be particularly explained with respect to its application to such a clutch actuation system.
FIG. 1 of the accompanying drawings shows a conventional clutch actuation system. A clutch pedal 2 drives a clutch assembly 1 via a cable assembly consisting of an inner cable 5 and outer cable 7. The clutch pedal 2 is pivoted on the body of a vehicle by a shaft 8 secured to the vehicle's body by a braket or the like. One arm 4 of the clutch pedal 2 is equipped with a pedal pad 6, so that it can conveniently be stepped on by the vehicle operator and depressed. The other end of the clutch pedal 2 is provided with a notch 14 which is engaged with the inner cable 5. A return spring 3 biases the clutch pedal 2 in the direction against the direction of pulling the inner cable 5, by bearing with its one end on the vehicle body 36 and with its other end on the arm 4 of the clutch pedal 2. A stop 24 is also fixed to the vehicle body, so as to oppose the movement of the arm 4 of the clutch pedal 2 and stop it rotating in the direction against the direction of pulling the inner cable 5 beyond a certain predetermined position.
The inner cable 5 extends through the outer pipe 7 to the actuating lever 9 of the clutch. This clutch 1 is of a well known sort, and comprises a flywheel 23 which is connected to an engine output shaft 27. A pressure plate 19 is mounted so as to oppose the flywheel 23 with a clutch facing 21 being between them. A circular spring or diaphragm 17 normally biases the pressure plate 19 against the flywheel 23, thus pinching the clutch facing 21 between them, and ensuring transmission of rotational power from the flywheel 23 to the clutch facing 21, which is rotationally connected to the output shaft 29. The release bearing 15 is so arranged that, when it is moved leftwards in the figure against the spring 17, it prevents pressure from being exerted by this spring 17 on the pressure plate 19, thus releasing the pinching of the clutch facing 21 and allowing the clutch to slip freely. This release bearing 15 is driven by the lever 9, which is pivoted at its lower end in the drawing to the body of the clutch assembly, and whose upper end is, as already stated, connected to the end of the inner cable 5.
Thus, to recapitulate, when the inner cable 5 is pulled, by the clutch pedal assembly, so that its lower end in the drawing moves leftwards in the drawing, it impels the lever 9 counter-clockwise, thus pushing the release bearing 15 leftwards in the drawing, and allowing the clutch to slip, be deforming the spring 17 about the point 25, and thus stopping the spring 17 from biasing the pressure plate 19.
The upper and the lower ends of the outer cable 7 are braced against the body of the automobile, and in the illustrated construction, the upper end is mounted adjustably, by several grooves 33 being formed on its joining portion, and by a circlip 35 being fitted into the grooves.
This kind of construction has several faults. The basic problems are:
(1) First, the inner cable 5 tends to stretch, which slackens it. Then, even if the clutch pedal 2 is completely depressed, it may occur that the clutch 1 does not slip completely, but drags; and, even if this extreme position is not reached, the travel of the clutch pedal 2 becomes unacceptably long. In other words, the point of control becomes too low, and may be beyond the travel of the clutch pedal.
(2) Second, as the clutch facing 21 wears, the spring 17 moves leftwards in the figure at its peripheral portions where it bears on the pressure plate 19, and therefore its inner portions move rightwards, so as to move the release bearing 15 rightwards; in other words, if the release bearing is moved from its extreme rightwards position in the figure to its extreme leftwards position, the point at which the clutch starts to slip becomes eariler and eariler, as the facing 21 wears. This has the effect of tightening the cable 5, which is the opposite effect to that described under (1). These two effects, although they are opposed, usually do not cancel each other out. If this second effect is dominant, the point of control becomes too high, and may be beyond the travel of the clutch pedal 2 in its upward direction; in other words, the stop 24 may prevent the clutch pedal 2 from being sufficiently raised to allow the clutch 1 to grip firmly, and therefore the clutch 1 will tend to slip at all times.
The usual way to cope with these problems is to adjust the outer pipe 7, as shown in the illustration. However, this requires frequent visits to a maintenance facility, which is exceedingly troublesome.
Various structures have been proposed for example, in Jap. Pat. Pubs. 23,128 and 23,129/77, and Jap. Utility Model. Pub. No. 44,499/73, for automatically adjusting the effective length of the inner cable, with respect to the outer pipe; however, they all have suffered from the disadvantage that the adjustment has taken place in a stepwise fashion, for example by adjusting gear means, and is not continuous. Therefore, fine adjustment has not occurred, and when, for example, the adjusting gear means is not properly engaged, erratic clutch operation may perhaps lead to an accident.
Similar clearance adjustment problems exist in other similar structures.